森林土壤融化期异养呼吸和微生物碳变化特征

采用室内土柱培养的方法,研究在不同湿度(55%和80%WFPS,土壤充水孔隙度)和不同氮素供给(NH_4Cl和KNO_3,4.5 g N/m~2)条件下,外源碳添加(葡萄糖,6.4 g C/m~2)对温带成熟阔叶红松混交林和次生白桦林土壤融化过程微生物呼吸和微生物碳的激发效应。结果表明:在整个融化培养期间,次生白桦林土壤对照CO_2累积排放量显著高于阔叶红松混交林土壤。随着土壤湿度的增加,次生白桦林土壤对照CO_2累积排放量和微生物代谢熵(q_(CO_2))显著降低,而阔叶红松混交林土壤两者显著地增加(P0.05)。两种林分土壤由葡萄糖(Glu)引起的CO_2累积排放量(9.61—13.49 g C/m~2)显著大于实验施加的葡萄糖含碳量(6.4g C/m~2),同时由Glu引起的土壤微生物碳增量为3.65—27.18 g C/m~2,而施加Glu对土壤DOC含量影响较小。因此,这种由施加Glu引起的额外碳释放可能来源于土壤固有有机碳分解。融化培养结束时,阔叶红松混交林土壤未施氮处理由Glu引起的CO_2累积排放量在两种湿度条件下均显著大于次生白桦林土壤(P0.001);随着湿度的增加,两种林分土壤Glu引起的CO_2累积排放量显著增大(P0.001)。单施KNO_3显著地增加两种湿度的次生白桦林土壤Glu引起的CO_2累积排放量(P0.01)。单施KNO_3显著地增加了两种湿度次生白桦林土壤Glu引起的微生物碳(P0.001),单施NH_4Cl显著地增加低湿度阔叶红松混交林土壤Glu引起的微生物碳(P0.001)。结合前期报道的未冻结实验结果,发现冻结过程显著地影响外源Glu对温带森林土壤微生物呼吸和微生物碳的刺激效应(P0.05),并且无论冻结与否,温带森林土壤微生物呼吸和微生物碳对外源Glu的响应均与植被类型、土壤湿度、外源氮供给及其形态存在显著的相关性。

Changes in heterotrophic respiration and microbial biomass carbon of forest soils during thaw

Packed soil core incubation experiment was made to study the effects of external carbon (C) (glucose, 6.4 g C/m²) addition on microbial respiration and microbial biomass C (MBC) in soils of a mature broadleaf and Korean pine mixed forest (BKPF) and an adjacent white birch forest (WBF) during thaw under different soil moisture levels (55% and 80% water-filled pore space) and nitrogen (N) supply (NH₄Cl and KNO₃, 4.5 g N/m²). The results showed that, without C and N addition, cumulative CO₂ flux from the WBF soil was significantly higher than that from the BKPF soil during the incubation period. With increasing soil moisture, the cumulative CO₂ flux and microbial metabolic quotient (q_CO2) decreased in the WBF soil but increased in the BKPF soil without C and N addition(P < 0.05). The glucose-induced cumulative CO₂ fluxes from the two forest soils ranged from 9.61 to 13.49 g CO₂-C/m², which was greater than the dose of added C in the form of glucose. The glucose-induced MBC in the two forest soils ranged from 3.65 to 27.18 g C/m², while glucose addition had little impact on soil dissolved organic C pool. Hence, the extra C released upon addition of glucose may result from the decomposition of soil native organic C. Without N addition and under the two soil moisture levels, the glucose-induced cumulative CO₂ flux from the BKPF soil was significantly higher than that from the WBF soil during thaw (P < 0.001). With increasing soil moisture, the glucose-induced cumulative CO₂ fluxes from the two forest soils were significantly increased (P < 0.001). The addition of KNO₃ alone significantly increased the glucose-induced cumulative CO₂ flux (P < 0.01) and the glucose-induced MBC (P < 0.001) in the WBF soil under two soil moisture levels (P < 0.001). Addition of NH₄Cl alone significantly increased the glucose-induced MBC in the BKPF soil with low moisture level. Based on the results from the previously reported non-freezing experiments and the results of the present study, it can be concluded that freezing treatment significantly affects the stimulating effects of glucose on soil microbial respiration and MBC under temperate forests. Regardless of whether freezing occurred or not, the responses of soil microbial respiration and MBC to the addition of extraneous C as glucose in temperate forests depend on vegetation type, soil moisture, and the amount and type of N added.